How much current can 12 AWG copper wire carry?

Per NEC Table 310.16, 12 AWG copper is rated 25 amps at 75°C and 30 amps at 90°C, but residential branch circuits with 12 AWG are limited to 20 amp breakers under NEC 240.4(D).

What is the difference between MCM and kcmil?

MCM and kcmil are the same unit: one thousand circular mils of conductor cross-section. MCM is the older abbreviation and kcmil is the modern one. 250 MCM and 250 kcmil describe identical conductors.

AWG Wire Gauge Chart

Diameter, cross-section, DC resistance, and NEC copper ampacity for every common wire size from 18 AWG through 1000 MCM. The complete American Wire Gauge reference table.

American Wire Gauge Reference Table

Size	Diameter (in)	Diameter (mm)	Area (cmil)	DC Resistance (Ω/1000 ft)*	Ampacity 75°C†	Ampacity 90°C†
18 AWG	0.0403	1.02	1,620	6.51	—	—
16 AWG	0.0508	1.29	2,580	4.09	—	—
14 AWG	0.0641	1.63	4,110	2.57	20 A	25 A
12 AWG	0.0808	2.05	6,530	1.62	25 A	30 A
10 AWG	0.1019	2.59	10,380	1.02	35 A	40 A
8 AWG	0.1285	3.26	16,510	0.641	50 A	55 A
6 AWG	0.1620	4.11	26,240	0.403	65 A	75 A
4 AWG	0.2043	5.19	41,740	0.253	85 A	95 A
3 AWG	0.2294	5.83	52,620	0.201	100 A	115 A
2 AWG	0.2576	6.54	66,360	0.159	115 A	130 A
1 AWG	0.2893	7.35	83,690	0.126	130 A	145 A
1/0 AWG	0.3249	8.25	105,600	0.100	150 A	170 A
2/0 AWG	0.3648	9.27	133,100	0.0795	175 A	195 A
3/0 AWG	0.4096	10.40	167,800	0.0630	200 A	225 A
4/0 AWG	0.4600	11.68	211,600	0.0500	230 A	260 A
250 MCM	0.5000	12.70	250,000	0.0423	255 A	290 A
300 MCM	0.5477	13.91	300,000	0.0353	285 A	320 A
350 MCM	0.5916	15.03	350,000	0.0302	310 A	350 A
400 MCM	0.6325	16.06	400,000	0.0264	335 A	380 A
500 MCM	0.7071	17.96	500,000	0.0212	380 A	430 A
600 MCM	0.7746	19.67	600,000	0.0176	420 A	475 A
750 MCM	0.8660	22.00	750,000	0.0141	475 A	535 A
1000 MCM	1.0000	25.40	1,000,000	0.0106	545 A	615 A

*Approximate DC resistance of uncoated solid copper at 20°C. Stranded and coated conductors read slightly higher. †Copper conductor ampacity per NEC Table 310.16 (not more than three current-carrying conductors in raceway, 30°C ambient). Small-conductor rules in NEC 240.4(D) cap overcurrent protection at 15 A for 14 AWG, 20 A for 12 AWG, and 30 A for 10 AWG copper. This chart is for reference only — verify against the NEC for your installation.

How AWG Works

American Wire Gauge runs backwards from what most people expect: the smaller the number, the bigger the wire. Each 3-gauge step doubles the cross-sectional area (and roughly halves the resistance), and each 6-gauge step doubles the diameter. Above 4/0 AWG ("four-aught"), sizes switch to MCM/kcmil — thousands of circular mils of cross-section.

Two numbers on this chart drive nearly every wire-sizing decision: ampacity (how much current the conductor can safely carry) and resistance (how much voltage you lose over distance). For short runs, ampacity usually governs. For long runs, voltage drop takes over — use our wire size calculator to check both at once.